The goal of this study is to assess and compare the hypothalmic-pituitary-adrenal axis (HPA) function in patients with idiopathic insomnia and hypersomnia related to another mental disorder whose chief complaint is daytime somnolence and whose degree of excessive daytime sleepiness has been objectively measured in the sleep laboratory. Our hypothesis is that idiopathic hypersomnia is associated with hypofunctioning of the HPA axis compared to another mental disorder and to normal controls.